Field of the Invention
The present invention relates to an organic light-emitting device, and more particularly, to an organic light-emitting device configured such that, particularly in a double-stack structure, emission layers of stacks have different characteristics in order to prevent an emission zone from being changed over time, whereby the lifespan of the organic light-emitting device is increased and the efficiency of the organic light-emitting device is improved, and an organic light-emitting display device using the same.
Discussion of the Related Art
Recently, with the advent of the information age, the field of displays that visually display electrically conveyed information signals has developed rapidly. In response to this, various kinds of flat panel display devices having excellent characteristics, such as a small thickness, a low weight, and low power consumption, have been developed and have rapidly replaced existing cathode ray tubes (CRTs).
Representative examples of such flat panel display devices may include a liquid crystal display (LCD) device, a plasma display panel (PDP) device, a field emission display (FED) device, and an organic light-emitting display (OLED) device.
Among these, the organic light-emitting display device is considered to have a competitive application because it does not require a separate light source and enables the realization of a compact device design and vivid color display.
Such an organic light-emitting display device includes self-luminous devices, such as organic light-emitting devices, provided in sub-pixels, and performs display via operation of the organic light-emitting devices on a per-sub-pixel basis. In addition, the organic light-emitting devices may be used as self-luminous devices in a lighting apparatus as well as the display device, and thus the development of organic light-emitting devices has recently been in the spotlight in the lighting industry. In addition, because the organic light-emitting devices require no separate light source unit, they are also advantageously used in a flexible display device or a transparent display device.
Meanwhile, an organic light-emitting device includes an organic emission layer between two electrodes. In addition, electrons and holes from the two electrodes are injected into the organic emission layer, and excitons are produced in the organic emission layer via combination of the electrons and holes. Then, when the produced excitons fall from the excited state to the ground state, light is generated from the organic light-emitting device.
Meanwhile, a stack structure including a plurality of organic emission layers provided between an anode and a cathode so as to be separated from each other on the basis of a charge generation layer has been proposed in addition to the above basic organic light-emitting device.
Generally, a stack structure is expected to express mixed colors of light and to improve light enhancement characteristics through the organic emission layers. However, light is energy having a wave motion. In the case in which the organic emission layers are provided, therefore, it is not simple to achieve both the expression of mixed colors of light and the improvement of light enhancement characteristics, and the specific design of the organic emission layers is important in the organic light-emitting device.
In the stack structure, each stack has a plurality of layers. When the organic light-emitting device is driven for a predetermined period of time, the mobility of holes and electrons supplied to each stack is changed. As a result, the emission zone formed in the emission layer located under the charge generation layer and the emission zone formed in the emission layer located above the charge generation layer may be changed over time. If such a change is extreme, electrons or excitons may accumulate at the interface between the emission layer and another layer adjacent thereto. In this case, the lifespan of the organic light-emitting device is greatly reduced, and the recombination rate of the excitons is reduced, whereby the efficiency of the organic light-emitting device is reduced.